So far, only the once per hour/booking. After some recent experiences, though, I'm beginning to think that it's as much psychological (lack of confidence sort of thing) as physiological/age-related (in my forties). Recovery time is typically more extended than, say, the ten minutes - tops! - needed in my twenties, which does induce a certain amount of pressure in a time-limited encounter, and also means I'm thinking about whether or not to pop early and risk not being able to go again, or hold back for one big one towards the end of the booking. Ideally, I'd like to manage twice - without being concerned about it - since I don't instantly lose interest as soon as I've cum; I still like to enjoy the girl's body and physical closeness throughout. If it was only about emptying my nuts, I'd just have a wank.